Artificial spinal discs have been used to replace native spinal discs that are diseased, injured or otherwise weakened. Examples of traditional artificial discs include articulating discs, wherein a disc implant typically has two halves that are pivotally connected to each other, and elastic discs, wherein an implant typically comprises one or more pieces of elastic materials, in some cases attached to endplates that are affixed to their respective vertebrae.
The elastic discs have an advantage over articulating discs in that the former in many cases provide more shock absorption and more closely approximate the motion states of a natural disc because modes of displacement are not limited to tilting. However, traditional elastic discs may experience certain failure modes that adversely affect the performance of the discs. For example, in elastic discs where the elastic material is attached to endplates that are affixed to the vertebrae, the elastic material may completely or partially detach from the endplates as a result of repeated tensile stress, thereby losing all or some of the tensile strength of the disc. Elastic materials themselves may deteriorate, by, for example, developing stress cracks, under tensile loading. In addition, certain elastic materials have more desirable properties under compressive loading than under tensile loading.
There is thus a need for an improved artificial disc utilizing elastic materials that reduces deterioration from tensile loading.